The present invention relates to a supercharged internal combustion engine of a motor vehicle, which has a cooling circuit, in which a working medium is recycled, which at least partially is conveyed in a vaporous or gaseous physical condition. In this connection, at least one expander unit is provided which is operatively connected with an output shaft of the internal combustion engine, in which the at least partially vaporous or gaseous working medium is expanded and the kinetic energy of the vapor or the gas is converted into kinetic energy.
With the development or further development of internal combustion engines, the main focus of the work recently, on the one hand, has been on the reduction of pollutants and on the other hand, on increasing efficiency of the assembly. In this connection, a possibility exists of increasing the efficiency of modern internal combustion engines by optimally using the heat occurring in the area of the respective internal combustion engine. By providing appropriate features, it is possible to limit the dimensions of the required cooling assembly as well as also make useable the heat loss for other applications in the area of the motor vehicle which otherwise is merely released to the environment. Until now, incidental heat in motor vehicles in the area of the internal combustion engine is used primarily for heating the interior of the vehicle. A problem with this, however, is that the heat required by the vehicle occupants varies, primarily, however, only in exceptional cases with the output provided from the combustion engine. In addition, in particular in the summer months, cooling rather than heating is required, whereby the cooling of the vehicle interior is realized with the aid of a corresponding cooling assembly.
In order to improve engine cooling, recently combustion engines, in particular, vehicle engines, were further developed, such that the corresponding systems enable a use of the incidental heat in the area of the internal combustion engine in the most effective manner. In this connection, on the one hand the possibility exists of using the incidental heat for other heat sinks provided in the vehicle or of converting the heat energy with the aid of corresponding circuit processes into mechanical energy, in particular, kinetic energy.
DE 197 45 758 A1 discloses a cooling assembly for internal combustion engines of motor vehicles, which are to make possible an optimal cooling of the combustion engine using proportionally smaller heat exchanger surfaces. The system described in this reference has an evaporative cooling system, in which the cooling water used, preferably a water-anti-freeze passes through a phase transition liquid-vapor-liquid during operation of the cooling system. In this connection, the effect is utilized that the heat transfer coefficients from the warm wall on the boiling liquid as well as from the vapor on the cold wall are higher than with the convection between liquid or gas and one wall. The use of the described evaporative cooling therefore should eventually ensure that heat exchangers can be used with relatively small heat exchanger surfaces compared to common convection heat exchangers. This leads to a substantial minimizing of the space required fro the cooling assembly, in particular the heat exchanger.
In addition to evaporative cooling, in which a substance, primarily water, which is mixed only with an additive for preventing freezing, is used in a coolant circuit, a cooling system for an internal combustion engine is disclosed for example in JP 09072255, which provides two cooling circuits, whereby in one of the two cooing circuits, a two-substance mixture is used as the working medium. In this connection, first incidental excess heat in the area of the internal combustion engine is conducted via a first cooling circuit and with the aid of a heat exchanger, transferred to the working medium supplied in the second cooling circuit. The working medium in the form of the two-substance mixture located in the second cooling circuit is a water-ammonia mixture. This mixture demonstrates in particular that the mixture components have different evaporation temperatures with the same pressure ratios. This type of system offers the advantage that already at a low temperature level, vapor is produced, which is available for a subsequent use.
In the described technical solution, essential components are provided in the second cooling circuit; a generator, in which the ammonia of the water-ammonia mixture is evaporated; a phase separator, in which the liquid phase is separated from the vapor phase; a condenser, in which the ammonia is again fluidized; a choke valve with a downstream evaporator; and finally an absorber, in which the gaseous ammonia is dissolved in water with heat output. In the described cooling system, the heat to be dissipated from the area of the internal combustion engine is transferred in the area of the generator to the water-ammonia mixture and finally used primarily with the help of the condenser for fuel preheating. Also in this case, based on the occurring phase transition, relatively small heat exchanger surfaces are used.
In addition, “BMW Power aus dem Abgas; in Auto Motor Sport from Dec. 8, 2005 (see also internet side http://www.auto-motor-sport.de/d/98231)” discloses a cooling system of a motor vehicle, in which heat energy is removed from exhaust and cooling water, which subsequently is converted in an expander unit into kinetic energy. The expander unit that is used has two steam-axial piston engines, which are coupled via a belt drive with the output shaft of the actual internal combustion engine. Also, this system has two separate cooling circuits for steam production, in which on the one hand water is heated to over 500° C. and on the other hand, ethanol is heated up to 105° C. Both media exist with the above-noted temperatures in the corresponding cooling circuits in the form of superheated steam, which is supplied respectively to one of the two steam-axial piston engines. The kinetic energy stored in the steam is converted in this manner into kinetic energy, which is transferred via the belt drive onto the output shaft of the internal combustion engine in order to achieve an increase in efficiency of the internal combustion engine.